Printing process



May5 ,1970. BLAKE ml. 13,510,340

PRINTING PROCESS Filed Oct. :5, 1966 STEP A STEP B BY GAS-LIQUID CONTACTCAUSE IMMEDIATE PRINT ON A HARDENING OF THE SUBSTRATE INK BY MEANS OF ABY LIQUID-LIQUID CONTACT rm A HARDENING CATALYST Q PEQ DIPPING SPRAYINGBY SOLlD-LIQUID CONTACT DUSTING RUPTURING CAPSULES INVENTORS CARL B.BLAKE y GEORGE K.L.TUNG

United States Patent 3,510,340 PRINTING PROCESS Carl B. Blake, Bronx,and George K. L. Tong, Richmond, N.Y., assignors to Martin-MariettaCorporation, New York, N.Y., a corporation of Maryland Filed Oct. 3,1966, Ser. No. 583,688 Int. Cl. B41m 1/26; B4411 1/02 US. Cl. 117-38 11Claims ABSTRACT OF THE DISCLOSURE A process of printing wherein an inkcontaining a binder made of an arcylate or methacrylate ester monomerboiling above about 185 C. and a compatible resin is deposited as alayer on a substrate and the deposited layer is contacted with apolymerization catalyst. Advantageously the monomer is selected from thegroup of acrylate and methacrylate diesters and triesters with diandpolyfunctional alcohols.

the ink employed in the process. The faster the ink dries,

the faster, within practical limits, the printing machinery can be runand subsequent operations carried out. As a printing operation speeds upand subsequent operations carrier out, a greater amount of productioncan be achieved per unit investment and consequent economic efficienciescan be obtained.

At the present time there are three principal types of rapid drying inkswhich for convenience will be termed newsprint type inks, heat set inks,and moisture set inks. Generally speaking, newsprint type inks comprisea pigment, for example, carbon black, dispersed in a nonvolatileoleogenous vehicle which does not dry in a physical or chemical sense.Rather the vehicle is absorbed by the medium upon which the print ismade. Heat set inks comprise pigments dispersed in a binder containingrelatively large amounts of hard resins and high boiling-point solvent.In use the heat set ink is printed onto a medium into which it is atleast partially absorbed. The .printed medium is then exposed to theaction of heat or flame which causes the high boiling-point olvents toevaporate and leave a hard, resin-bonded pigmented film. Moisture setinks generally contain a pigment dispersed in a vehicle comprising aresin and a solvent. As produced, the resin is soluble in the solventand the solvent has the capability of dissolving water. When the resinsolvent mixture is substantially anhydrous, a homogeneous, singlephasesolution is obtained. However, if the solvent of the mixture ispermitted to absorb water, the resin precipitates and a two-phase,solid-liquid system results. In use, the moisture set ink is printedupon an absorbent medium. Initially, the medium absorbs a portion of theliquid binder. Directly following printing, the printed medium isexposed to a fine spray of water or an atmosphere of steam. Immediatelyupon this exposure, the resin precipitates forming a solid-phase binderfor the pigment. The combination of the actions of precipitation andabsorption result in rapid hardening of the printing ink film.

Each of the aforementioned rapid drying types of inks have an area ofpractical utility which is, at present, being exploited by the printingindustry. However, each of the 3,510,341 Patented May 5, 1970aforementioned types of inks has certain disadvantages. To anyone whohas handled a newspaper the principal disadvantage of thenewsprint-types of inks is obvious. The ink deposit is easily rubbedfrom the surface of the paper. In addition, newsprint-type inks areadapted to be printed only on highly absorbent stock, thus limiting thequality of paper which can be used with them.

Heat-set inks have a number of disadvantages. For example, the cost ofheaters of sufficient capacity to provide a relatively high temperaturein a short period of time is high. If the ink is to be dried rapidly,for example within four seconds after printing, temperatures as high as180 C. must be used. Such temperatures have a deleterious affect onpaper such that a meaningful proportion of the natural strength of thepaper is lost and an undesirable artificial aging of the paper occurs. Afurther disadvantage of heat-set inks lies in the fact that evaporatedsolvent vapors constitute a fire hazard.

Additional problems have now presented themselves with respect to use ofheat-set inks. Currently, heat-set inks are used extensively inhigh-speed web operations and the vapors resulting therefrom are ventedto the atmosphere. The solvent vapors given off by the printing unitsmay be accured of contributing to smog formation. In general, proposedregulations with respect to solvent dispersal into the atmosphere divideorganic solvents into two classes, i.e. (a) those which are harmful inthemselves and (b) those considered not to be harmful in themselves.Proposed regulations do not apply to the aforementioned (h) group solong as such solvents are used at temperatures of F or lower. Normalheat-set operations employ inks containing high boiling-point solventsin order to avoid fire and explosion hazards in the press room. Asstated before, temperatures as high as C. (356 F.) are needed to assurequick ink setting. In some instances, the printed surfaces are evensubjected to flame impingement in order to harden the ink. Accordingly,it is likely that smog control regulations will be applied to printersusing large volumes of heat-set inks even though, for the most part, thesolvents used in the inks do not in themselves contribute to smogformation.

With respect to moisture-set inks, difiiculties have arisen by virtue ofthe fact that the inks provide little gloss when dry and they are notadaptable to the printing of finely detailed letters or designs.Moisture-set inks are poorly adaptable for printing on relativelynonporous surfaces, such as high gloss paper. The particular chemicalnature of the moisture-set systems generally dictates the use ofrelatively high cost solvents such as glycols. Further, as the initialink setting takes about four minutes, the printing industry has foundthe average maximum speed of printing is somewhere in the nature of 650feet per minute. Thus while newsprint inks, heat-set inks, andmoistureset inks have definite areas of utility, they are not, in anysense of the word, a panacea for the need of the printing industry foran instantaneous drying ink, i.e. an ink which will dry to a tack-freesurface in a maximum of about five seconds after drying is initiated.

It has now been discovered that by means of a special combination ofoperations a novel process can be provided wherein a freshly printedsurface can be hardened within a few seconds to provide anoffset-resistant printed sheet without danger of expelling significantquantities of potentially dangerous solvent vapors.

It is an object of the present invention to provide a novel printingprocess.

A further object of the present invention is to provide a novel processof printing characterized by rapid hardening of a freshly printedsurface.

A still further object of the present invention is to provide a meanswhereby drying of specially formulated printing inks can be accomplishedin a matter of seconds.

Another object of the present invention is to provide a novel printingink.

Other objects and advantages of the present invention will becomeapparent from the following description taken in conjunction with thedrawing in which the figure shows in schematic outline the process ofthe present invention.

Generally speaking, the present invention contemplates a process forprinting which comprises depositing a layer of flowable, induratableprinting ink on a substrate which ink exhibits the viscosity andtackiness necessary to assure adhesion to said substrate and contactingsaid ink with a hardening catalyst, said ink and siad catalyst havingcharcteristics such that hardening of the ink occurs substantiallyinstantaneously, that is, within a few, e.g. up to four, or five,seconds after contact with the catalyst.

Inks useful in accordance with the present invention are generallycharacterized by containing a substantial proportion of a monomericsubstance or substances capable of polymerizing in the presence of acatalyst and a resin compatible therewith by being substantially free ofpermanent solvent and by having rheological properties suitable for usewith the type of printing operation which is employed. To be suitablethe monomeric substance is ordinarily a liquid at room temperature, hasa relatively high boiling point, e.g. in excess of about 185 C. and alow polymerization potential as defined hereinafter. Ordinarily an inksuitable for use in the present process will be free of permanentsolvent, that is a solvent which does not react to form a solid or doesnot evaporate readily from printed surfaces. It is advantageous for themonomer to act as the solvent in the ink and disappear by virtue ofpolymerization. However, it is possible to include in the ink smallamounts of volatile solvents provided such solvents evaporate from theprinted ink film under printing conditions, e.g. at a temperature ofless than 125 F., within a few seconds after printing. The rheologicalcharacteristics required in the ink will depend, for the most part, onthe type of equipment used for printing. For example, a suitable gravureink will have a viscosity of a fraction of a poise and a low yield valueof the order of 4 dynes per square centimeter. A suitable letterpressink used on a cylinder-platen machine could have a viscosity of about200 to 800 poises and a yield value of the order of about 2000 dynes persquare centimeter. An ink suitable for a sheet-fed rotary ofiset processmight exhibit a viscosity of about 400 to 2000 poises and a yield valueof the order of 10,000 dynes per square centimeter. The layer of inkwhich is deposited is generally between about 1 to 35 microns thick and,more advantageously, between about 2 and microns in thickness. Since anink generally contains a dispersed pigment and is very often depositedupon a substrate such as paper which is capable of draining more or lessof the liquid phase away from the pigment, the actual layer thicknesswhich must be hardened substantially instantaneously is probably notmuch more than two microns thick per printing operation. Of course, itis within the contemplation of the present invention to print more thanone layer and to harden the plurality of layers in one hardeningoperation.

Contact with the catalyst can be accomplished in a number of differentways. The catalyst can be dissolved in a solvent. The solution can thenbe applied to the printed substrate by spraying or by dipping. When asolvent is used to dissolve the catalyst, care must be taken inselecting the solvent such that it does not deleteriously alfect theprinted surface. The solvent should also evaporate from the substratewithin a few seconds, i.e. less than five seconds under conditions ofprinting, i.e. at a temperature of less than 125 F. to leave thehardened printed film in a substantially solvent-free condition.Alternatively, the catalyst in the form of a powder can be dusted ontothe substrate either before or after printing. Advantageously,

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the catalyst can be encapsulated in micro-capsules. The ink can containthe micro-encapsulated catalyst and, after printing, the micro-capsulescan be broken by application of energy such as pressure, infraredexposure (or other form of heat) or ultra-sonic energy or the ink can beexposed to vapors which tend to weaken or disintegrate the capsulewalls. It is also possible to precoat the substrate withmicro-encapsulated catalyst and to rely on the pressure normallyassociated with printing to both deposit the ink and rupture thecapsules in the printed areas. Further, it is within the contemplationof the present invention to employ a gaseous phase catalyst which isbrought into contact with the printed sheet after printing has beencompleted. The various means by which the process of the presentinvention can be carried out are illustrated schematically in thedrawing. Referring now thereto, the drawing shows the first step of theprocess (step A) to be printing on a substrate. The printing can consistof a single layer of printing ink or a plurality of layers such as isnormally laid down in a multicolor printing operation. The substrate canbe paper, cardboard, plastic sheet, cellophane, metal foil, textile orany other substrate which is conventionally printed using ordinaryprinting machinery. The second step (step B) of the process comprisescausing immediate hardening of the ink by means of a hardening catalystspecifically selected to cooperate with the ink to produce a tack-freesurface in a maximum of about five seconds after contact is made. Thecatalyst can be a gas, a liquid or a solid which is brought into contactwith the liquid ink layer or layers. If the catalyst is soluble in aliquid solvent, contact can be effected by means of dipping or spraying.If the catalyst is a solid, contact can be accomplished by applying thesolid as a dust to the printed surface. Set forth on the drawing as aspecies of solid-liquid contact is the process involving rupturing ofcapsules. A catalyst enclosed in micro-capsules can be a liquid or asolid and, as mentioned hereinbefore, can be either a constituent of theink or can be applied separately. The indication of thecapsule-rupturing species under solid-liquid contact in the drawingrefers primarily to the contact between the liquid ink layer and theinterior of capsules having solid-phase walls.

An advantageous, rapidly induratable ink composition in accordance withthe present invention comprises a binder containing a high viscosityvarnish and a polymerization accelerator which varnish and acceleratormixture is adapted to rapidly react to form a solid when brought intocontact with a free radical generating catalyst, e.g. a peroxide-typecatalyst. Generally, a pigment and a waxlike additive are incorporatedinto the varnish-accelerator binder to provide specific printing inkcharacteristics. Normally, the varnish, the accelerator, the pigment andthe wax-like additive are present in amounts within the following ranges(in percent by weight):

One of the outstanding novel and advantageous features of the presentinvention, i.e. the rapid drying (or hardening) character of an inkcomposition, such as tabulated above, is a function primarily of thebinder, i.e. the varnish, taken in association with the accelerator.Essentially the varnish comprises a polymerizable monomer and a resin.The amounts of the respective ingredients are such that the monomer isat least equal in weight to the resin and the combination of the twoingredients provides a varnish having the characteristics required forthe printing operation contemplated. For example, a varnish suitable forletterpress inks should have a viscosity of about Z, to Z as measuredwith the Gardner Bubble Viscometer.

An example of a satisfactory varnish in accordance with the presentinvention in percent by weight is as follows:

Percent Trimethylolpropane trimethacrylate 50.5 Diethylene glycoldiacrylate 38.0 Cellulose acetate butyrate 11.5

Such a varnish is made by stirring the cellulose acetate butyrate resininto the monomer mixture at room temperature until it is dissolved.Satisfactory results have been attained when one or more of ethyleneglycol dimethacrylate, triethylene glycol dimethacrylatc, polyethyleneglycol dimethacrylate, butylene glycol diacrylate, 1,6-hexamethyleneglycol diacrylate, 1,6-hexamethylene glycol di methacrylate,trimethylolpropane triacrylate, cyclohexyl acrylate, propylene glycolmonoacrylate or methacryloxyhydroxy soy oil monomer is or are used inplace of the mixed acrylate and methacrylate esters employed in theforegoing example. Likewise, satisfactory results are attained when oneor more compatible, monomer-soluble resins such as hard acrylic resin,lacquer resin, chlorinated rubber, ethyl cellulose or a rosin ester isor are used in place of cellulose acetate butyrate resin employed in theforegoing example. In general, the varnish comprises from about 55% to95% by weight of monomer with the balance essentially resin.Advantageously, for good printing characteristics the varnish containsabout 75% to 85% by weight of monomer. Ordinarily no solvent other thanthe monomer is present in the varnish.

From the aforementioned illustrative species of monomers and resinsuseful in manufacturing advantageous printing ink varnishes inaccordance with the present invention, certain generalizations can bemade. Thus, monomers useful in the varnishes and printing inks of thepresent invention have an unsaturated carbon-tocarbon linkage inconjugated relationship with a carbonyl group and include acrylic andmethacrylic esters having a molecular weight of at least about 150 whenthe ester molecule contains no free hydroxyl group and a molecularweight of at least about 130 when the ester molecule contains at leastone free hydroxyl group. Resins useful in accordance with the presentinvention are those which are soluble (dispersible) in and compatiblewith said monomer.

To be useful at all in the process of the present invention, a monomerin the presence of a catalyst must be characterized by exhibiting apolymerization potential (hereinafter defined) of less than about 20seconds at 25 C. For practical purposes the most highly advantageousmonomers have a polymerization potential of less than about seconds at25 C. In order to be operati-ve for purposes of the present invention,monomers must also have a relatively low vapor pressure, e.g. of theorder of about 1 millimeter of mercury (mm/Hg) at about 20 C. Generallyin line with the low vapor pressure, a monomer operative in accordancewith the present invention will have a boiling point of at least about185 C. at 760 mm. pressure. Further, monomers useful in accordance withthe present invention are compatible with and do not deleteriouslyaffect rubber and other organic materials usedin the construction ofprint ing machinery. As a general rule, the requirements of the presentinvention as to monomers will be satisfied by diesters or triesters ofacrylic acid and/or methacrylic acid with glycols, trimethylolpropane,trimethylolethane, pentaerythritol, etherified glycols, glycerol and/orhydroxylated vegetable oils.

For purposes of this specification and the claims appended hereto, theterm polymerization potential is defined as the time in seconds for astandard quantity of monomer to polymerize under standard catalyzedconditions. In determining the polymerization potential at 25 C., thefollowing procedure was carried out:

A. ten gram sample of monomer was taken to which was added 1.0 gram of a20% by weight solution of 2,4-dichlorobenzoyl peroxide in acetone. Themonomer and peroxide were mixed for 30 seconds. Then 0.2 gram ofN,N-dimethyl-p-toluidine was mixed into the catalystmonomer composition.Time for polymerization to occur (the polymerization potential) wasmeasured from the time of the addition of the tertiary aromatic amine.An illustration of the importance of the actual determination of thepolymerization potential and the difficulty in predicting the speed ofpolymerization of monomers under the conditions prevailing in thepresent invention is the difference in polymerization potential at 25 C.between cyclohexyl acrylate and cyclohexyl methacrylate. Cyclohexylacrylate has a polymerization potential at 25 C. of 5 seconds whereascyclohexyl methacrylate does not polymerize under the aforestatedconditions at 25 C. Since it is an object of the present invention toprovide printing inks which will be instantaneously hardenable at roomtemperature, the polymerization potential at room temperature (25 C.) isa highly used too]. However, since low wattage radiant heaters and thelike can be used to rapidly raise the surface temperature of paper by asmall amount, for example, up to about 50 C. or even C., thepolymerization potential at temperatures between room temperature and 80C. of monomers for use in the compositions of the present inventionshould be less than about 20 seconds.

In using the inks of the present invention in printing, it is requiredthat after the ink is deposited on the surface being printed, there mustbe contact between the ink and a free-radical generating catalyst, e.g.a peroxide catalyst. Advantageously, for operation at 25 C. orthereabout, the peroxide catalyst is 2,4-dichlorobenzoyl peroxide ordecanoyl peroxide. Other catalysts which may .be used include benzoylperoxide, tertiary dibutyl hydroperoxide, methyl ethyl ketone peroxideand methyl ethyl ketone hydroperoxide. The peroxide catalyst can beapplied to the ink deposit either by dipping or by spraying or. by othermethods disclosed herein'before. In the case of either dipping orspraying, it is necessary that the catalyst be dissolved in a solventwhich does not disturb the printed matter and which evaporates from theprinted substrate substantially immediately at temperatures of less thanabout F. Excellent results in this regard have been attained with acatalyst solution containing 2.0% by weight of Luperco CDB (a paste of50% by weight 2,4-dichlorobenzoyl peroxide in dibutyl phthalate), 20% byweight of ethyl acetate and 78% by weight of normal hexane. An even moreadvantageous catalyst solution comprises, by weight, 2% decanoylperoxide, 20% ethyl acetate and 78% hexane. It is believed that theperoxide catalyst reacts rapidly with the accelerator in the ink toproduce free radicals and thus initiates and propagates thepolymerization of the monomer with little or no induction period.Regardless of the theoretical mechanism, it has been found that in orderfor the present invention to be operative, the ink ordinarily mustcontain an accelerator, for example, an aromatic tertiary amine such asN,N-dimethyl-p-toluidine, dimethyl-otoluidine and N,N-dimethylaniline inan amount of about 0.8% to 6% by weight of the varnish. Lessadvantageously, an oxidizable metal soap, such as cobalt naphthenate,can be used in relatively large amounts as an accelerator.

In compounding inks useful in the process of the present invention, onecan employ as pigments any of the usual pigmentaceous materials commonto the printing ink art. Such pigmentaceous materials include pigmentssuch as carbon black, titanium dioxide, chrome yellow, molybdate orange,milori blue, phthalocyanine blue, lithol red, permanent red 2B,extenders such as calcium carbonate, silica, aluminum hydrate, hydriteclay, magnesium carbonate, blanc fixer, toners such as methyl violet,alkali blue, and other materials commonly employed to attain specialeffects and advantages.

7 In carrying out the present invention it is advantageous to employ aletterpress ink composition as set forth in Table I.

TABLE I Weight percent Monomer 45-73 Resin 735 Total varnish 7584Pigment 11-21 Accelerator 0.5-3 Wax l2 Specific examples of letterpressinks useful in accordance with the present invention are set forth inTable 11.

TABLE II Example No 1 2 3 4 Wt. percent trimethylol propanetrimethacrylate 39. 3 40. 2 27. 5 26. 8 Wt. percent diethylene glycoldiacrylate 29. 6 30. 2 21. 20. 4 Wt. percent cellulose acetate butyrate-8. 9 9. 1 3. 3 3. 2 Wt. percent lacquer resin" 31. 6 30. 8 Wt. percentpowdered polyethylene 1. l. 5 1. 6 1. 6 Wt. percent N,N-dimethyl-p-toluidine. 2.0 2. 0 1. 1 0. 6 Wt. percent permanent red 2B18. 7 10. 4 Wt. percent milori blue 3.0 Wt. percent carbon black 14. 0Wt. percent phthalocyanine blu Wt. percent aluminum silicate...

Resin sold by Archer-Daniels-Midland under commercial designationArochern 650.

Essentially the letterpress inks are made by preparing a varnish,milling pigments and wax (polyethylene) into a major portion of thevarnish, mixing the remainder of the varnish with the amine acceleratorand incorporating the mixed accelerator and varnish with the pigmentedvarnish. In all ink formulations within the ambit of the presentinvention powdered polyethylene can be replaced in substantially equalamounts by microcrystalline wax, paraffin wax or any one of a number ofnatural or synthetic waxy materials. Such wax-like additives areconventionally used in printing inks to improve the working propertiesof the inks, to eliminate picking of the stock being printed, to reduceink tack, to prevent set off, mottle, crystallization and skinning, toimpart enhanced scuff resistance and to improve rub-resistance.

As mentioned hereinbefore, the inks of the present in vention areprinted on the stock and the printed stock is then contacted with aperoxide catalyst. Conveniently, this contact may be accomplished byspraying with an ultra-fine spraying. The peroxide catalyst isadvantageously dissolved in a solvent mixture such as ethyl acetate andhexane. The ethyl acetate can be replaced by low-boiling aromatichydrocarbon, by ketones or by other esters. Hexane can be replaced byother low-boiling aliphatic hydrocarbons and/ or halogenatedhydrocarbons. When the catalyst contacts the ink deposit, immediately,e.g. within about 1 to about 5 seconds, the surface of the ink depositbecomes hard. Within a few more minutes the ink sets throughout itsthickness. The surface hardened ink can be overprinted and is ruband setoff-resistant almost immediately. While the inks of the presentinvention are shelf stable and may in the usual case be kept up to aboutsix months in storage, it is advisable both during manufacture andstorage to avoid heating the inks or the varnishes on which they arebased in order to minimize chances of premature polymerization.

While the present invention has been described in conjunction withpreferred embodiments, modifications and variations may be resorted toas those skilled in the art will recognize. Such modifications andvariations are considered to be within the purview and scope of theinvention.

1. A process of printing comprising (A) depositing on a substrate alayer of printing ink,

(B) said ink comprising a binder consisting essentially of about 55% to95% by weight of a liquid monomer selected from the group of acrylateand methacrylate esters having boiling points in excess of about 185 C.and polymerization potentials less than about twenty seconds attemperatures up to about 80 C. with the balance being essentially aresin compatible therewith and a small amount of an accelerator, and

( C) contacting said layer of printing ink with a peroxide catalystcapable of generating free radicals whereby said layer of printing inkhardens substantially instantaneously.

2. A process as in claim 1 wherein the layer of printing ink iscontacted with a catalyst in a readily evaporable liquid phase.

3. A process as in claim 1 wherein the layer of printing ink iscontacted with a solid phase catalyst.

4 A process as in claim 1 wherein the layer of printing ink is contactedwith a catalyst by rupturing capsule Walls enclosing said catalyst.

5. A process as in claim 1 wherein the monomer is selected from thegroup consisting of acrylic and methacrylic diesters and triesters withglycols, trimethylolpropane, trirnethylolethane, pentaerythritol,etherified glycols, glycerol and hydroxylated vegetable oils and theaccelerator is an aromatic tertiary amine.

6. A process as in claim 1 wherein the catalyst is decanoyl peroxide.

7. A process as in claim 1 wherein the layer of printing ink iscontacted with a catalyst in liquid phase.

8. A process as in claim 1 wherein the ink binder contains about to byweight of the monomer.

9. A process as in claim 1 wherein the layer of printing ink iscontacted with a catalyst by rupturing capsule walls enclosing saidcatalyst.

10. A process as in claim 1 wherein the monomer in the ink binder has apolymerization potential of less than about 5 seconds at a temperatureof about 25 C.

11. A process as in claim 10 wherein the layer of printing ink iscontacted with a catalyst in solid phase.

References Cited UNITED STATES PATENTS 3,240,619 3/1966 Eichel 11736.83,317,433 4/ 1967 Winchester 117-38 FOREIGN PATENTS 698,689 1964-Canada.

ALFRED L. LEAVITT, Primary Examiner M. F. ESPOSITO, Assistant ExaminerUS. Cl. X.R.

